• 동력기계공학회지
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• 제17권4호
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• pp.45-50
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• 2013

This paper presents the comparison of heat transfer and pressure drop of various secondary refrigerants (single-phase and two-phase) in the indirect refrigeration system. The main results were summarized as follows: In case of heat transfer, it is useful to use secondary refrigerants in low evaporating temperature region and the heat transfer coefficient of single-phase is larger than two-phase secondary refrigerants. In case of pressure drop, it is useful to use secondary refrigerants in high evaporating temperature region and the pressure drop of two-phase is smaller than single-phase secondary refrigerant. Also, $CO_2$ is the best useful because pressure drop of $CO_2$ among the secondary refrigerants is the smallest.

• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.65-74
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• 2004

The heat transfer coefficient and pressure drop of $CO_2$(R-744) during gas cooling Process of carbon dioxide in a horizontal tube were investigated experimentally and theoretically. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop consist of a receiver. a variable-speed pump. a mass flowmeter, an evaporator. and a gas cooler(test section). The main components of the water loop consist of a variable-speed Pump. an constant temperature bath. and a flowmeter. The gas cooler is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus The test section consists of smooth, horizontal stainless steel tube of 9.53 mm outer diameter and 7.75 mm inner diameter. The length of test section is 6 m. The refrigerant mass fluxes were 200 ~ 300 kg/($m^2{\cdot}s$) and the inlet pressure of the gas cooler varied from 7.5 MPa to 8.5 MPa. The main results were summarized as follows : The predicted correlation can evaluated the R-744 exit temperature from the gas cooler within ${\pm}10%$ for most of the experimental data, given only the inlet conditions. The predicted gas cooley capacity using log mean temperature difference showed relatively food agreement with gas cooler capacity within ${\pm}5%$. The pressure drop predicted by Blasius estimated the pressure drop on the $CO_2$ side within ${\pm}4.3%$. The predicted heat transfer coefficients using Gnielinski's correlation evaluated the heat transfer coefficients on the $CO_2$ side well within the range of experimental error. The predicted heat transfer coefficients using Gao and Honda's correlation estimated the heat transfer coefficients on the coolant side well within ${\pm}10\;%$. Therefore. The predicted equation's usefulness is demonstrated by analyzing data obtained in experiments.

• 한국생산제조학회지
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• 제22권3_1spc호
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• pp.551-557
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• 2013

The heat transfer performance and pressure drop characteristics of brazed-plate heat exchangers with 20 and 30 plates were experimentally measured and analyzed in this study. The mass flow rates of the heat exchangers with 20 and 30 plates were fixed at 0.6 and 0.9 kg/s for the low temperature side, respectively. The mass flow rate for the high temperature side was controlled from 0.2 kg/s to 1.2 kg/s. The inlet temperatures for the high and low temperature sides were $10^{\circ}C$ and $7^{\circ}C$, respectively. The heat transfer characteristics were not influenced by the number of plates. The pressure drop at the heat exchanger with 30 plates was slightly higher than that with 20 plates. The values calculated from the correlations based on gasket plate heat exchangers were compared with the experimental results. It was found that the predicted Nusselt numbers for the gasket plate heat exchangers were about 5% to 20% lower than the measured Nusselt numbers for the brazed plate heat exchangers. However, a pressure drop comparison showed that the calculated pressure drops at the gasket plate heat exchangers were less than half of the measured pressure drops at the brazed plate heat exchangers.

• 설비공학논문집
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• 제7권1호
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• pp.132-141
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• 1995

Characteristics of pressure-drop oscillations(PDO) in a boiling channel were studied numerically and compared with experimental data. Effects of initial and boundary conditions on PDO were investigated in terms of oscillation period and amplitude. The period and amplitude of PDO increased with increasing of the compressible volume in the surge tank and the heat input. PDO occurred within the specific range of the fluid temperature, at which oscillation period and amplitude diminished rapidly with the increase of the fluid temperature. The increase of the loss coefficient in fluid supply line resulted in slightly longer oscillation period and larger amplitude. Numerical results showed good agreement with the experimental data.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.172-177
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• 2005

The object of this experiment is comparing heat transfer performance and pressure drop characteristics by baffle cut rate, fluid velocity and heating temperature. Experiments were carried out in cross flow heat exchanger with water as a working fluid. In this experiment, baffle cut rate is 30%, 40%, 50%, velocity is 0.5m/s, 1.0m/s, 1.5m/s, and heating temperature is $30^{\circ}C$, $40^{\circ}C$, $50^{\circ}C$. An experimental device to measure the heat transfer coefficient was constructed. The experimental result were obtained for the fully developed turbulent flow of water in tube on the condition of uniform heat flux.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1141-1146
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• 2009

Experimental investigation on two-phase flow boiling heat transfer of R-410A and R-134a in horizontal small tubes is reported. The pressure drop and local heat transfer coefficients were obtained over heat flux range of 5 to $40\;kW/m^2$, mass flux range of 70 to $600\;kg/m^2s$, saturation temperature range of 2 to $12^{\circ}C$, and quality up to 1.0 in test section with inner tube diameters of 3.0 and 0.5 mm, and lengths of 2000 and 330 mm, respectively. The section was heated uniformly by applying a direct electric current to the tubes. The effects of mass flux, heat flux, and inner tube diameter, on pressure drop and heat transfer coefficient are presented. The experimental results are compared against several existing correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in small tubes is developed.

• 설비공학논문집
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• 제20권5호
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• pp.357-363
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• 2008

In order to investigate $CO_2$ heat transfer coefficient and pressure drop by PAG oil concentration during $CO_2$ evaporation, the experiment on evaporation heat transfer characteristics in a horizontal micro-fin tube was performed. The experimental apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiment was conducted for various mass fluxes($400{\sim}1200\;kg/m^2s$), heat fluxes($10{\sim}30\;kW/m^2$) and saturation temperatures ($-5{\sim}5^{\circ}C$), and PAG oil concentration($0{\sim}5\;wt%$). The variation of the heat transfer coefficient was different in accordance with the oil concentration. With the increase of the oil concentration, the evaporation heat transfer coefficient decreased and the delay of dryout by oil addition was found. Pressure drop increased with the increase of the oil concentration and heat flux, and the decrease of saturation temperature.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1440-1446
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• 2012

본 논문은 수평 마이크로핀관내 초임계 $CO_2$와 PAG 혼합물의 열전달과 압력강하 특성에 대해서 실험적으로 연구한 것이다. $CO_2$와 PAG 혼합물의 열전달계수는 압력이 10 MPa이고, 질량유속은 520 kg/$m^2s$이며, PAG 오일 농도는 0.06~2.26%에서 측정하였다. PAG 오일농도가 0.3%인 경우, $CO_2$와 PAG 혼합물의 열전달계수와 압력강하는 순수 $CO_2$ 냉매의 열전달계수와 동일한 경향을 나타내었다. 그리고 PAG 질량농도가 2.26%인 경우, 초임계 온도근처에서 측정한 열전달계수는 순수 $CO_2$의 열전달계수 보다 약 50%정도 낮게 나타났다. 마찰압력강하는 $60^{\circ}C$의 $CO_2$ 평균온도에서 순수 $CO_2$의 압력강하보다 약 1.6배 더 높게 나타났다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.1199-1204
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• 2006

The pressure drop and heat transfer coefficient were measured at room temperature in CFB heat exchanger with multiple vertical tubes. Also the circulation rate of solid particles was measured. The theoretical model for predicting heat transfer coefficient using the solid flowrate was developed in this study. The model predictions were compared with the measured heat transfer coefficient to show relatively good agreement.

• 설비공학논문집
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• 제11권4호
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• pp.472-483
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• 1999

The evaporation heat transfer and pressure drop characteristics for HFC-l34a in flat plate type heat exchangers with enhanced beads were experimentally investigated. Three plate type evaporators with different geometric condition of U-turn area were tested. Mass fluxes were tested over the range of 83kg/$m^2$s to 166kg/$m^2$s, and heat fluxes were varied from 4㎾/$m^2$ to 12㎾/$m^2$. Evaporation temperature was 5$^{\circ}C$ with inlet qualities of 0.1 to 1.0. There was no notable difference in the heat transfer coefficient by geometric variation of U-turn area, but the third plate with cross-ribbed channel at U-turn area was better than others in the evaluation using volume goodness factor comparison. Also, the mixtures of HFC-l34a and PAG oil was tested to determine oil effects on heat transfer and pressure drop. As oil concentration was increased, heat transfer coefficient was increased by 22~48% up to the 3wt.%, but decreased by 14~22% at the 4wt.%. The pressure drop was increased by the maximum of 100% as oil concentration was increased.